-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
RCaffin
Not wrong planet - wrong galaxy.
Cheers
Roger
Right?
Heaven forbid that someone should use a professional EDA package instead of the industry's equivalent of Duplo.
In a more bridge-building, happy light, though, here's a suggestion:
mcdowswe, if you have the time would you mind adding some files to the github project? In particular, if you can do a generate & export of gerber files for the PCBs, anyone can get them made pretty much anywhere. A PDF export of the schematics would mean those without Altium would also be able to trace things down. If all anyone wants to do is make boards per your design a little bit cheaper this'd be all they needed.
And it would mean that anyone who wanted to modify the design for themselves would be able to create (and, obviously, publish in the spirit of open source) an Eagle format mirror of the design files.
-
Totally Awesome
Macdowswe,
Your work is totally awesome, even better than a triple chocolate custard filled bismark!
I would also like to thank Websrvr for all his generous contributions and personally wish him happy holidays.
Santa will visit soon and all the children will be happy too.
Live from downtown Burbank home of the world famous Christmas Kringle.
JoeyB
Quote:
Originally Posted by
macdowswe
https://cdn.hackaday.io/images/2665861480778750936.jpg
The time has finally come for the manufacturing run of ODrive v3.1. They are now on the way, and should arrive early to mid January.
At this stage, around 20 board kits are going out the people who signed up to the "Inital development" phase. They have not been all allocated yet, you can signup
here.
Since the boars are going out to just a small group of early developers, I will have the time to personally get you up to speed with the codebase and help to get going with the hardware. Then, together, we can prepare some stuff that is a bit more stable and a bit more documented for when the alpha testing begins.
The cost for me to get this small batch of boards manufactured was $96 per board, so that is the amount I need to ask for a kit, plus shipping.
The kit involves basically everything seen in the above picture, and consists of:
- ODrive v3.1
- USB Programmer
- A set of the optional large gauge wire screw terminals
- A set of pin headers
- Some nylon standoffs
I hope that ODrive will be able to help you make an awesome robotics project, thank you so much for your contribution to helping people have access to open robotics hardware and software.
-
Re: Open source low cost servomotor controller
Hi websrvr
To explain: this is a hobby project one person is running, and he is running it HIS WAY, as is his right.
It might fly, or it might not. It might be too expensive, or it might not. But it is HIS project.
Since it is HIS project, he is at liberty to publish how he wants and as much or as little data as he wants. That is HIS choice.
For anyone else to come along and try to take the project over and dictate how data should be made available is not only wrong, it is impolite and futile.
My 2c
Cheers
Roger
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
aarggh
I couldn't see it anywhere but are you planning on producing 3 axis boards?
Very cool looking project, major props getting it out there!
cheers, Ian
Hey, thanks!
So yeah many people have requested a 3 axis version, and the plan is to do that for v4. I have already identified a microcontroller that has the peripherals required for that.
Cheers,
Oskar
-
Re: Open source low cost servomotor controller
So on the topic of websrvr's offer and the resulting discussion:
I am intending to make the price point lower than $96, as I already stated previously in the thread, the target price is around $50.
I have many different options to chose from, including one guy over at the OpenPnP mailing list who offered to manufacture 50 boards for free to get the project started.
I chose to go with CircuitHub to get some prototype boards done quickly.
Can we please keep the topic of the thread about not this now?
How about: What kind of forces are required to do CNCing on your machine? Do you use leadscrews or belts?
Cheers,
Oskar
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
dharmic
Right?
Heaven forbid that someone should use a professional EDA package instead of the industry's equivalent of Duplo.
In a more bridge-building, happy light, though, here's a suggestion:
mcdowswe, if you have the time would you mind adding some files to the github project? In particular, if you can do a generate & export of gerber files for the PCBs, anyone can get them made pretty much anywhere. A PDF export of the schematics would mean those without Altium would also be able to trace things down. If all anyone wants to do is make boards per your design a little bit cheaper this'd be all they needed.
And it would mean that anyone who wanted to modify the design for themselves would be able to create (and, obviously, publish in the spirit of open source) an Eagle format mirror of the design files.
So the schematic pdf is already available on GitHub: Link.
Yeah other people have already asked for gerbers. The reason I haven't provided them yet is because there are still some bugs in the hardware design, that I hope will be fixed with version 3.1 (the one currently being manufactured). Only when I have verified that the bugs are solved will I be comfortable in recommending others to manufacture boards of their own.
Cheers,
Oskar
-
Re: Open source low cost servomotor controller
Champion, Oskar. And thank you for your efforts with this design - and for deciding to share it with us. Very generous of you!
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
macdowswe
So on the topic of websrvr's offer and the resulting discussion:
I am intending to make the price point lower than $96, as I already stated previously in the thread, the target price is around $50.
I have many different options to chose from, including one guy over at the OpenPnP mailing list who offered to manufacture 50 boards for free to get the project started.
I chose to go with CircuitHub to get some prototype boards done quickly.
Can we please keep the topic of the thread about not this now?
How about: What kind of forces are required to do CNCing on your machine? Do you use leadscrews or belts?
Cheers,
Oskar
Hi we use 4nm motors on our mills and lathes if that helps
Gesendet von iPad mit Tapatalk
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
Tkamsker
Hi we use 4nm motors on our mills and lathes if that helps
Gesendet von iPad mit Tapatalk
Cool!
How difficult would it be for you to install a motor that was 1Nm, but could spin 4 times faster?
Would this be a dealbreaker?
-
Re: Open source low cost servomotor controller
Hi
difficult not but depending on the prices of motors. The issue is normal the power curve we use Nanotec st6018 L3008 now and to get similar curve i need an bigger motor than https://granitedevices.com/store/bl7...th-cables.html or Welcome to Delta Group we would end up in 750W range. We do lathes and mills for steel (similar to torch or Novakon ) but really build in europe no china stuff ! so the advantage of servo is that it can turn around 2k-3k RPM compared to stepper 0,52 - 0,75k And looking at the curves there is a power gap (similar to 2 stroke engines ;)- if we overcome that i would be verry interested. thomas
-
1 Attachment(s)
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
Tkamsker
Hi
difficult not but depending on the prices of motors. The issue is normal the power curve we use Nanotec st6018 L3008 now and to get similar curve i need an bigger motor than
https://granitedevices.com/store/bl7...th-cables.html or
Welcome to Delta Group we would end up in 750W range. We do lathes and mills for steel (similar to torch or Novakon ) but really build in europe no china stuff ! so the advantage of servo is that it can turn around 2k-3k RPM compared to stepper 0,52 - 0,75k And looking at the curves there is a power gap (similar to 2 stroke engines ;)- if we overcome that i would be verry interested. thomas
So I had a look at the stepper you are using, and it has the following speed/torque profile:
Attachment 343774
I calculated the mechanical power capability at the selected point, and it turns out to be 17W. If you check the table of motors I made at the bottom of the motor post on the project page (link), you can see that they can deliver a much higher power, and they are very inexpensive. For instance, the Turnigy Aerodrive SK3 - 4250-350kv will run relatively cool at 0.7Nm, and it will happily run up to 7k RPM.
So basically, the inexpensive brushless motors are not as high torque, but they make up for it by being much faster, and able to deliver full torque through the whole speed range, and hence being much higher power.
-
Re: Open source low cost servomotor controller
Hi,
thank you i see the data funny the Link i use is Nanotec: ST6018 Schrittmotor - NEMA 24 We never run the motors faster than 562.2 RPM because of the power delivered. We also need some force to decelerate our mill. I am sure (or not sure depends ) that the motor your mentioned has much lower braking resistance as we need for our application. But in the hopefully quiet time i will have a look on the data you mentioned ,.. i am not sure they can deliver the flu torque around the full speed range but it may be worth a check ,.. and you have col project on rout hp thumbs up
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
Tkamsker
Hi,
thank you i see the data funny the Link i use is
Nanotec: ST6018 Schrittmotor - NEMA 24 We never run the motors faster than 562.2 RPM because of the power delivered. We also need some force to decelerate our mill. I am sure (or not sure depends ) that the motor your mentioned has much lower braking resistance as we need for our application. But in the hopefully quiet time i will have a look on the data you mentioned ,.. i am not sure they can deliver the flu torque around the full speed range but it may be worth a check ,.. and you have col project on rout hp thumbs up
Yeah when it comes to deceleration, the motors are not very high friction, so you will need to actively brake the motors. The resulting energy absorbed can be either dumped into a brake resistor, or if you use a battery, you can charge the battery.
Thanks, I hope it can be useful!
Cheers,
Oskar
-
Re: Open source low cost servomotor controller
I think $96 is rather reasonable for a two driver board. Anyone who has priced a commercial brushless servo driver from companies like Parker, Applied Motion, Copley, AMC will pay a couple hundred more for a single driver solution. $48 per driver is rather cheap. I'm actually interested since I have a couple of larger CMC brushless motors that have peak current well over 35amps. My Applied Motion brushless drivers are max 14amps. The 24 volt supply voltage is the limiting factor. I have to look up the Kv parameter to see what rpm the motor can achieve with only a 24volt supply.
-
Re: Open source low cost servomotor controller
Ho Oskar,
I was thinking about this project and I really think to get some critical mass you should target the 6040 purchasers. The 6040's all come with a non-functioning crappy blue box TB6560 based controller, and usually the only good option is a G540, which puts it seriously over budget for a lot of people. A 3 axis (or 2 x 2) controller with a "cheat sheet" on hooking it up for these machines will be an instant target market for you I believe.
If your solution is coming in around half the cost of the G540, it seems your ideally positioned for taking this quite large segment on head on which no other vendor is doing now!
cheers, Ian
-
Re: Open source low cost servomotor controller
A 2 axis board at that prices would be good for useing it as a coil winder motor controller, or a small lathe
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
aarggh
Ho Oskar,
I was thinking about this project and I really think to get some critical mass you should target the 6040 purchasers. The 6040's all come with a non-functioning crappy blue box TB6560 based controller, and usually the only good option is a G540, which puts it seriously over budget for a lot of people. A 3 axis (or 2 x 2) controller with a "cheat sheet" on hooking it up for these machines will be an instant target market for you I believe.
If your solution is coming in around half the cost of the G540, it seems your ideally positioned for taking this quite large segment on head on which no other vendor is doing now!
cheers, Ian
However these 6040 type cnc's come with steppers. Converting to servo motors isn't a hard task but the cost of drivers, servo motors, encoders, motor mounts etc. will be atleast the cost of a gecko540 I would think.
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
macdowswe
So on the topic of websrvr's offer and the resulting discussion:
I am intending to make the price point lower than $96, as I already stated previously in the thread, the target price is around $50.
I have many different options to chose from, including one guy over at the OpenPnP mailing list who offered to manufacture 50 boards for free to get the project started.
I chose to go with CircuitHub to get some prototype boards done quickly.
Can we please keep the topic of the thread about not this now?
How about: What kind of forces are required to do CNCing on your machine? Do you use leadscrews or belts?
Cheers,
Oskar
I think you have a good idea for a much needed product and I'm hoping you are successful in meeting your goals and hopefully provide a final product that is a transition away from stepper motors.
Leadscrews, ballscrews, belts along with machine size, drag and mass all have different motion/drag coefficiencies and the HP to weight ratio is more important when offsetting cutting forces when selecting a drive to make it move so you can't get results from a CNC machine and use them as a blanket statement/value representing all machines.
Now, I believe this project is targeting the home/hobby/DIY users who really need a solid solution but the off-chance that you could grab a large portion of the 6040 market is unrealistic considering that not only would they need to purchase the board, they would need to purchase motors with encoders, fabricate mounts for their specific machine and power supplies as well and the only person I know who produces inexpensive BLDC servo motors isn't a business and doesn't stock or sell them to the general public so waiting to hear about an up-coming production run is on my monthly to-do list so I don't miss out as I stash a small collection of suitable BLDC servo motors and if I had an extra $13K I could spare for a year I'd just make my own production run (200pcs) and sell the BLDC servo motors on ebay.
Of course I've seen the DIY 2500KV and 3500KV outrunners motors reworked to add an encoder or hal sensors which seem suitable for router type machines but even this is an expensive solution unless you have the motors and encoders laying around.
I purchased 5pcs of a single axis 10A (25A peak) 60V STM32F1 based servo driver including heatsink for cheap and have the eagle files for them, so I am able to produce the board for cheaper than I paid but the issue is I have no firmware because the guy who created it isn't sharing it or giving it out and I'm not a programmer so I've set the files aside for a later time since I was also able to get my hands on 3pcs of the assembled board for free which don't have any firmware and the ones with firmware are set up so you can't dump the firmware from them to write to the empty boards.
Adding additional axis would cost roughly $10.00 per axis or less in a small quantity run so your driver in 3, 4 or 5-axis is very possible if the hardware is reworked as needed.
According to my friend, one of the major design issue is related to FET current/peak current and requires alterations, use different FET's, copper thickness should be 3oz minimum and to allow for higher peak current based on trace surface area and thickness, stopping the trace would allow you to use up to a 6A noload current motor which will typically have up to 30A peak current requirement depending on it's design and intended use, bigger inertia motors have lower RPM and are more suited to axis driving but low inertia motors will have faster acceleration and provide significantly higher rapids due to the higher achievable RPM so there is some flexibility/trade-off depending on the machines mechanical limitations but also consider, the cost of a decent (such as Tamagawa) 10KRPM encoder is about $100.00, a decent (such as Tamagawa) 16KRPM encoder is about $160.00 and a decent (such as Tamagawa) 20KRPM encoder is around $200.00, luckily I have a source for 16KRPM A/B/Z encoders for $31.00ea so high speed incremental encoders isn't an issue I have to deal with.
Your PDF schematic reference schematics not in PDF format so it couldn't be properly examined however, from the available PDF schematic he says it doesn't look like the motor encoder signals utilizes complimentary or balanced input signals (+/-) thus advising, adding something like a MAX3097ECSE encoder receiver which supports A+/A-/B+/B-/Z+/Z- input signals with single ended A/B/Z outputs and includes outputs for individual encoder signal errors and a combined encoder error output line so you can drive LED's for individual (A/B/Z) error lines and use the combined error line to notify the MCU that the encoder has an error requiring you to look at the board to see which encoder signal is at fault which could be open, shorted, missing pulses etc...
Because they can't wait for you to finish the design to obtain something for their own lathe project, someone else following this project has decided to create Eagle v7.7.0 files and he's paying my friend to fix the major electrical issues and sadly he has no desire to share the files he creates at his expense so no one else can benefit and this sucks because I think it's selfish but I do understand his logic since he's paying to get it for his own use and not interested in sharing at his expense.
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
aarggh
Ho Oskar,
I was thinking about this project and I really think to get some critical mass you should target the 6040 purchasers. The 6040's all come with a non-functioning crappy blue box TB6560 based controller, and usually the only good option is a G540, which puts it seriously over budget for a lot of people. A 3 axis (or 2 x 2) controller with a "cheat sheet" on hooking it up for these machines will be an instant target market for you I believe.
If your solution is coming in around half the cost of the G540, it seems your ideally positioned for taking this quite large segment on head on which no other vendor is doing now!
cheers, Ian
Quote:
Originally Posted by
jfong
However these 6040 type cnc's come with steppers. Converting to servo motors isn't a hard task but the cost of drivers, servo motors, encoders, motor mounts etc. will be atleast the cost of a gecko540 I would think.
I checked ebay very briefly, and I found that there are kits available without any motors or controllers for $800, Link, and that kits with motors, driver, spindle and spindle driver are about $1300, Link. Supposing someone currently has to spend $300 on a G540 on top of the full kit (totaling $1600) to get a usable system, that leaves a $800 space to compete in.
One approach is to just buy a VFD and a spindle motor, and subtract that off the $800 margin, and start from there. For the motion, I know there exist appropriate motors, appropriate dirt cheap encoders, and the missing piece would be some mechanical bits to put it all together.
However, in a more interesting scenario, we go one step further: We could use two ODrives: three channels for motion and the 4th channel to drive the spindle. For the spindle, you could do something like this: Link.
In both cases, I think we have a chance to do something interesting here ;D
Cheers,
Oskar
-
1 Attachment(s)
Re: Open source low cost servomotor controller
websrvr makes a very good point about the ability of the copper foil on a PCB to support the peak currents. Take note of his concerns.
I have met problems here myself. It's not just the current carrying ability, its also about how you connect TO the copper. Abrupt transitions between heavy connectors and light foil can be problematic, as shown here (commercial unit):
Attachment 343960
I did wonder why the driver had stopped working!
But there were other faults on the PCB as well. Eventually I replaced the 3 units with 3 Gecko drivers.
Anyhow, there are design guides on the web for the current carrying capacity of copper tracks.
Cheers
Roger
-
1 Attachment(s)
Re: Open source low cost servomotor controller
This 6,000 r.p.m. encoder also looks promising and can be found for $25.00 or less.
See the data sheet for more info.
JoeyB
-
Re: Open source low cost servomotor controller
Care needed here.
Those encoders are only quoted to 2000 ppr, which is 500 lines/rev, and a maximum of 100 kHz output. Those are fairly basic specs. Yes, the bearings can take 6,000 RPM, but you won't be getting any signal at that speed.
Cheers
Roger
-
Re: Open source low cost servomotor controller
Roger,
Will the encoders I posted work reliably within the r.p.m. limitations of a 5tpi ballscrew?
JoeyB
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
joeybagadonuts
Roger,
Will the encoders I posted work reliably within the r.p.m. limitations of a 5tpi ballscrew?
JoeyB
The encoder should go on the motor. Not the screw. With fast turning motors it is unlikely they would be direct drive. For a 7000 rpm motor, you would probably have about a 4:1 ratio.The screws can take upwards of 2500 rpm depending on size. If geared 4:1 then the motor could be spinning upwards of 10,000 rpm. So you could exceed the rpm capabilities of that particular encoder.
-
Re: Open source low cost servomotor controller
109jb,
Correct me if I am wrong. Pulleys and belts or some sort of gear reducers would add a lot of cost to this arrangement?
I was under the assumption this was going to be some sort of low cost project.
JoeyB
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
macdowswe
I checked ebay very briefly, and I found that there are kits available without any motors or controllers for $800,
Link, and that kits with motors, driver, spindle and spindle driver are about $1300,
Link. Supposing someone currently has to spend $300 on a G540 on top of the full kit (totaling $1600) to get a usable system, that leaves a $800 space to compete in.
One approach is to just buy a VFD and a spindle motor, and subtract that off the $800 margin, and start from there. For the motion, I know there exist appropriate motors, appropriate dirt cheap encoders, and the missing piece would be some mechanical bits to put it all together.
However, in a more interesting scenario, we go one step further: We could use two ODrives: three channels for motion and the 4th channel to drive the spindle. For the spindle, you could do something like this:
Link.
In both cases, I think we have a chance to do something interesting here ;D
Cheers,
Oskar
Those are worst case 6040's which barely meet the rigidity requirements however, stiffeners on the gantry sides help and replacing the lower outer frame assembly for a steel version and the machine improves but cutting 7075-T6 becomes problematic since the table isn't rigid enough to take the down force due to the individual extrusion strips used to make up the table, solid aluminum T's bolted to a 7/16in cold-rolled steel plate solves that problem and adding a couple more rail supports stops the rail flex during plunging.
I also don't think those specific 6040's are worth the cost since I can get a solid table and cast frame kit for $200.00 more but if you're really hard up for cash it's a good starting place if you're willing to do some modifications.
Personally I'd go to a larger DIA round rail or use HiWin 4-way loading linear rails on a 3/8in cold rolled flat-stock (with stiffeners) lower frame assembly so cutting mild steel is possible and use one of Dale Walsh's integrated air-cooled 220V 3KW BT20 ATC spindle with 2500PPR encoder (I think he still makes it) or maybe a cheap water cooled 2.2KW ISO20 ATC spindle from china.
Enough about frames, back to ODrive and package variants.
Since some gantry machines like the 6040 and larger employ dual drives to move the gantry to prevent skewing, perhaps adding two jumpers wouldn't be a bad idea so that a single axis signal (such as y-axis) can drive both motors (daisy-chain) and the second jumper to invert the direction signal of the secondary channel (so both sides of the gantry move in the same direction) which is good for dual belts, rack and pinion and dual ballscrew gantry setups.
-
Re: Open source low cost servomotor controller
Pulleys and belts or some sort of gear reducers would add a lot of cost to this arrangement?
Everything adds cost. Everything.
Whether the cost of belts and pulleys would be worth while would depend almost entirely on what specs you want. For sure, toothed belts are usually cheaper and work better than gears.
Cheers
Roger
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
joeybagadonuts
109jb,
Correct me if I am wrong. Pulleys and belts or some sort of gear reducers would add a lot of cost to this arrangement?
I was under the assumption this was going to be some sort of low cost project.
JoeyB
These type motors have the power, but at higher rpms, not at low rpm. They are going to need some kind of reduction system to operate efficiently. If the example 7000 rpme motor is capable of 1kW, that is about 190 oz-in. If we assume a perfectly flat torque curve that means it only has 192 oz-in of torque at low rpm too. So, I'd say that motor needs a belt reduction or something on it. A belt drive doesn't have to cost a lot. I have 2 belt drives on my current stepper project and the timing belts and sprockets were bought on e-bay for about $12 per set. A suitable set of pulleys and belts for this type of servo drive would probably be a bit more money, but certainly less than about $30 per set.
I personally don't envision this as a lower cost than a stepper system, or even the same cost as a stepper system, but rather a low cost for the potential performance. As far as servo drives go I think it has that potential at a much lower cost than other servo drive systems and am watching the development to see how it flushes out.
-
Re: Open source low cost servomotor controller
RCaffin &109jb,
Thank you for taking the time to explain in layman's terms, it's refreshing to get a positive point of view.
JoeyB
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
RCaffin
websrvr makes a very good point about the ability of the copper foil on a PCB to support the peak currents. Take note of his concerns.
I have met problems here myself. It's not just the current carrying ability, its also about how you connect TO the copper. Abrupt transitions between heavy connectors and light foil can be problematic, as shown here (commercial unit):
Attachment 343960
I did wonder why the driver had stopped working!
But there were other faults on the PCB as well. Eventually I replaced the 3 units with 3 Gecko drivers.
Anyhow, there are design guides on the web for the current carrying capacity of copper tracks.
Cheers
Roger
Thanks for the heads up.
I have tried to make sure that there is as much copper as possible in the current path that is expected to carry the motor current. The copper track impedance going around the motor current loop is approximately 1 milli ohm. This is 5 times smaller than the impedance through the MOSFETs in the same current path, so hopefully the amount of copper should be fine.
I have designed the board so that you can add a single heatsink for all the MOSFETs. There is also a thermistor placed as close as possible to each of the MOSFET group (3 thermistors total). The control algorithms will also have thermal control, so hopefully it should be fine with the current design. Of course if it turns out that things get too hot, we can always beef up the tracks at the cost of a larger PCB, or thicker copper at the cost of price.
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
109jb
These type motors have the power, but at higher rpms, not at low rpm. They are going to need some kind of reduction system to operate efficiently. If the example 7000 rpme motor is capable of 1kW, that is about 190 oz-in. If we assume a perfectly flat torque curve that means it only has 192 oz-in of torque at low rpm too. So, I'd say that motor needs a belt reduction or something on it. A belt drive doesn't have to cost a lot. I have 2 belt drives on my current stepper project and the timing belts and sprockets were bought on e-bay for about $12 per set. A suitable set of pulleys and belts for this type of servo drive would probably be a bit more money, but certainly less than about $30 per set.
I personally don't envision this as a lower cost than a stepper system, or even the same cost as a stepper system, but rather a low cost for the potential performance. As far as servo drives go I think it has that potential at a much lower cost than other servo drive systems and am watching the development to see how it flushes out.
I agree that the motors will run more efficiently if you do something like 4:1 reduction gearing. But I am interested in discussing what defines the torque requirements. My hypothesis is that you need a lot more torque on a stepper system because you have to deal with even the shortest load spikes with a decent margin to avoid skipping steps under all circumstances. However, with closed loop encoder feedback, I think you can be completely fine with a fraction of the torque.
As an example, suppose you had 4Nm of torque on a 5mm pitch ball-screw, that gives 8kN of force. I am not very familiar with machining, but I don't think you persistently need almost a ton of force for most applications.
That said, efficiency is ofc better to run things cooler, so it may be a good idea to use reduction anyway.
Cheers,
Oskar
-
Re: Open source low cost servomotor controller
Greatest torque requirements tend to be when accelerating up to speed. This is completely dependent on the specific machine, and the performance that the user is looking for. If you want 1G accel rates, then you'll need a lot more torque than if you're fine with 0.1G accel.
This seems like it might be a nice solution for a small, high performance machine.
-
Open source low cost servomotor controller
http://uploads.tapatalk-cdn.com/2016...04e540f435.jpg
I posted this picture awhile back in another thread......
Here are some motors I have for comparison sake and the continuous torque rating for them. You can see the BLDC motors have much more continuous torque than a similar sized brushed servo. Why do I have so many? Some of these are spares for existing machines and others will be used for not yet completed ones. ALL have been purchased for under $40 each on eBay, most were around $25. The biggest one #12, was only $25 shipped!!! All work and most of them are actually new.
1. Nema17 stepper motor. 76oz-in. Size found in most 3D printers
2. Brushed servo Yaskawa minertia T01l. 13.9oz-in.
3. BLDC servo Parker CM162. 56oz-in
4. Nema23 stepper motor. 286oz-in. Typical stepper size
5. BLDC servo CMC BNL2310. 100oz-in
6. BLDC servo Parker CM231. 46oz-in
7. Brushed servo Clifton. 46oz-in
8. Brushed servo Minertia T06m. 96oz-in
9. Brushed servo Minertia RM-04sa. 59oz-in
10. Brushed servo Electrocraft E661. 140oz-in
11. BLDC servo CMC BNR3312. 198oz-in
12. BLDC servo CMC BMR4445. 722oz-in. Huge motor!!!
Running a servo motor past its continuous torque rating for any length of time will overheat and could damage it, not recommended to do. The 276oz-in stepper motor is pretty small compared to most of the servos and puts out quite a bit more low speed torque than most of these servos do. This is where pulley reduction for servo motors is quite useful. 3:1 or 4:1 reduction will surpass the low speed torque of the stepper motor and give lots more peak torque for machine acceleration.
Most of these motors are rated to spin at 3000rpm or more. Some of the brushless ones go 10k. With 3:1 reduction, you can still spin a leadscrew 1000rpm. A stepper motor torque starts to drop pretty fast when it spins more than a few hundred rpm. Big advantage to servo motors when you need higher leadscrew rpm.
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
macdowswe
I agree that the motors will run more efficiently if you do something like 4:1 reduction gearing. But I am interested in discussing what defines the torque requirements. My hypothesis is that you need a lot more torque on a stepper system because you have to deal with even the shortest load spikes with a decent margin to avoid skipping steps under all circumstances. However, with closed loop encoder feedback, I think you can be completely fine with a fraction of the torque.
As an example, suppose you had 4Nm of torque on a 5mm pitch ball-screw, that gives 8kN of force. I am not very familiar with machining, but I don't think you persistently need almost a ton of force for most applications.
That said, efficiency is ofc better to run things cooler, so it may be a good idea to use reduction anyway.
Cheers,
Oskar
For small machines like 3d printers, smaller routers, etc, that run on low friction linear rails, you probably could run without a reduction drive as the motor is likely very much overkill. I tend to think more along the lines of milling machines running on dovetail slides that can have a fair amount of friction, and machine heads weighing 50 pounds or more moving vertically at 200 IPM. In those cases, I would surely want the reduction drive for efficiency. Once I get some more funds I intend to buy a unit, motors, and encoders and try it on my mill with the hopes that I can boost the rapids and push up acceleration. As mentioned, the highest torque required is accelerating. I think the motor that you previously showed is more than enough, but at 1kW max at 7000 rpm it is around 190 oz-in. I currently have 570 oz-in steppers and they will stall right off the bat at essentially 0 rpm with the acceleration turned up. I currently have acceleration at 40 in/sec^2 to keep that from happening, or about 0.1g. So if it is taking about 570 oz-in to accelerate at 0.1g then you could surmise that it would be 1140 oz-in to accelerate at 0.2g. With the motor you linked that would be about 6:1 reduction based on 190 oz-in. At max speed for the motor at 7000 rpm the screw would turn 1166 rpm which would give me 233 IPM feed rate. So theoretically I can use that motor and boost my rapid traverse speed a little, but the big benefit is doubling my acceleration. For my machine 233 IPM is plenty, but better accel for certain machining operations would be welcome. That would likely be pushing that little motor to its limits during accel.
-
Open source low cost servomotor controller
Finding higher pulley ratio gearing wasn't all that cheap at the time when I did my z axis on my small bench mill. I went 4.5:1 using gt2 pulleys. 20tooth 8mm bore for the motor and 90tooth 1/4" bore for the ballscrew. The 90tooth was the expensive one. I think I paid almost $40 with shipping just for that one pulley from stock drive products. If you find a cheaper source, let me know.
Edit I actually wanted 5:1 or 6:1 but I recall not finding a larger pulley that had 1/4" bore or something like that. It was a few years ago.
-
Re: Open source low cost servomotor controller
For example, this 4:1 ratio gt2 pulley and belt set is $17 with free shipping
3D Printer GT2 60T 15T Belt 6mm Timing Pulley Belt set kit Reduction Ratio 4:1 | eBay
For larger than 60T gt2 belts you would likely need to order them from a specialty house at higher cost, but even at 4:1 I can get a theoretical improvement on my current mill. From my previous example of my machine I would have 760 oz-in of available torque from the Turnigy motor, so I could increase accel from 0.1g to 1.33g and get 350 IPM rapids, with the benefit of a closed loop system. Since it is closed loop I could probably get a bit higher accel than with the stepper since the stepper accel needs more torque reserve margin than a servo would. Also, this is with the motor that was linked as an example. Other motors could be used that have a lower kv and would operate at lower RPM.
-
Open source low cost servomotor controller
Thanks for the link. I haven't seen that. Although I don't think the 15 tooth pulley has enough there to bore it out to fit my 8mm shaft. Probably why I choose 20 tooth at the time.
Edit Some of my servo motors have 3/8" or larger shaft diameter. Getting a 4:1 pulley set that fits without spending $$ isn't easy. It costs more for the pulleys than the motor!!!
-
Re: Open source low cost servomotor controller
A few questions I have about the drive:
1. It uses a battery as a reserve for high load motions to stabilize the bus voltage. I think this is a pretty smart way of doing it, butt the battery linked on the Odrive page shows a 3S Lipo, does it have to be a 3s Lipo battery or can other size/type batteries be used. For example, a 12V car/motorcycle/lawn tractor battery?
2. If it has to be a Lipo, is there protection from overcharging? I have seen Lipo batteries combust and it isn't pretty
3. The documentation says that the bus voltage is 24V. Is the system using a step up converter to achieve this?
-
Open source low cost servomotor controller
Quote:
Originally Posted by
109jb
For example, this 4:1 ratio gt2 pulley and belt set is $17 with free shipping
3D Printer GT2 60T 15T Belt 6mm Timing Pulley Belt set kit Reduction Ratio 4:1 | eBay
For larger than 60T gt2 belts you would likely need to order them from a specialty house at higher cost, but even at 4:1 I can get a theoretical improvement on my current mill. From my previous example of my machine I would have 760 oz-in of available torque from the Turnigy motor, so I could increase accel from 0.1g to 1.33g and get 350 IPM rapids, with the benefit of a closed loop system. Since it is closed loop I could probably get a bit higher accel than with the stepper since the stepper accel needs more torque reserve margin than a servo would. Also, this is with the motor that was linked as an example. Other motors could be used that have a lower kv and would operate at lower RPM.
For comparison sake I'm using 46oz-in continuous torque brushed servo/gecko320, 5tpi ballscrew, 4.5:1 pulley. The continuous leadscrew thrust is 410lbs, the peak leadscrew is almost 1400lbs. 110ipm. If the specs on the Turnigy motor are as advertised, I think you will have more than enough torque and acceleration.
The original setup was 276oz-in steppers with geckodrive. Easily stall out stepper when plunging/drilling operations. With the servo setup, I have to worry about the spindle stall if I go to fast. Plenty of torque for my machine.
-
Re: Open source low cost servomotor controller
Quote:
Originally Posted by
jfong
Thanks for the link. I haven't seen that. Although I don't think the 15 tooth pulley has enough there to bore it out to fit my 8mm shaft. Probably why I choose 20 tooth at the time.
Edit Some of my servo motors have 3/8" or larger shaft diameter. Getting a 4:1 pulley set that fits without spending $$ isn't easy. It costs more for the pulleys than the motor!!!
Yeah. the larger shaft sizes will require larger sprockets. The little RC motor that we have been talking about is a 5mm shaft, so works well for this set of sprockets.